1. Field of the Invention
The present invention relates to a method and a device for filling particles of a solid catalyst uniformly into a tubular reactor. The invention also relates to a device for carrying out the method.
2. Description of the Related Art
It is known that tubular chemical reactors comprise typically several hundred to several thousand vertically arranged tubes.
The filling of these tubes with particles of solid catalyst is of great importance since the conditions and results of the reaction, which will be carried out in the reactor in the presence of the catalyst (for instance, the manufacture of ethylene oxide, aniline, etc.), depend significantly on the uniformity and homogeneity of the filling of the different tubes.
During the filling, empty spaces may be formed between the grains of catalyst within the tubes, thus creating, during the exothermal reaction, hot points on said tubes, which are prejudicial to the metallurgy of said tubes. Furthermore, the charge of the reactor can pass by way of preference through poorly filled tubes, resulting in poor operation of the reactor and therefore a poor yield of the industrial unit.
Summarizing, it can be said that a poor filling of the tubes results in a reduction in the useful life of the reactor and in more frequent intervention for maintenance, resulting in interruptions in the production cycle.
In order to obtain a uniform filling of the tubes, it has therefore been proposed that the filling of the catalyst be effected tube by tube (see EP-A 041 144 or equivalent U.S. Pat. No. 4,461,327!), possibly arranging accessories in the tubes in order to facilitate the distribution of the particles of catalyst within them (see, for instance, EP-A 548 999 or equivalent U.S. Pat. Nos. 5,247,970! or 3,608,751).
It has also been proposed to effect the filling of the reactor by series of tubes (for instance of 10 to 20 tubes), as described in U.S. Pat. No. 3,913,806 or JP-A 59/139 923.
Finally, in order to accelerate the filling of the catalyst particles, it has also been proposed to vibrate the feed receptacles, as described in FR-A 2 691 954 or GB-A 1 267 086 or equivalent U.S. Pat. No. 3,700,140!.
However, these methods have the drawback of requiring extremely long filling times, of using complicated and bulky filling machines, of requiring the presence of several operators and of leading, despite everything, to appreciable differences in density of filling between the tubes of one and the same reactor.
The present invention is directed at overcoming these drawbacks of the prior art by recourse to known homogeneous filling methods and devices of the "dense filling" type, which are already used in catalyst-bed chemical reactors. These techniques are described, for instance, in EP-A 007 854 or equivalent U.S. Pat. No. 4,306,829!, EP-A 116 246 or equivalent U.S. Pat. No. 4,564,328!, and French Patent Application No. 95 12334 of Oct. 21, 1995 or equivalent U.S. patent application Ser. No. 08/735,373!.
It is known that these so-called dense filling techniques employ a substantially uniform distribution of the catalyst particles by a rain effect, these particles being poured into the upper part of the reactor onto a generally mobile unit driven in rotation (comprising, for instance, circular sectors or flexible thongs), thus permitting a substantially uniform distribution within the reactor.
In the course of different jobs, which consisted in applying these techniques for the uniform distribution of a solid in divided form to the filling of tubular reactors, it was found that the tubes located furthest to the outside of the tube plate are filled faster than those located in the central part of the reactor. The tube plate of the reactor should be understood to be the metal plate which connects the different tubes together at their upper part and which is arranged substantially perpendicular to said tubes. It follows that, if this filling is continued, the accumulation of the particles is accentuated at the site of the filled tubes located furthest to the outside of the tube plate. This accumulation of particles causes, by overflow, a non-dense filling of the tubes in the course of filling, which are located nearer the center of said tube plate.
Furthermore, it is known that if the particles of catalyst are fragile, one frequently encounters risks of attrition of these particles when they fall on the tube plate of the reactor.